Wheel support device, suspension system and vehicle comprising the said support device

ABSTRACT

A support device connects a wheel to suspension elements of a vehicle, the wheel having a radius R′. The support device includes rods articulated at their lower ends to the suspension elements and at their upper ends to the wheel carrier so as to confer on the wheel a degree of camber freedom relative to the suspension elements. The camber movement takes place around an instantaneous center of rotation. The device is also configured in such manner that Y and Z are respectively the abscissa and ordinate of the instantaneous position of the instantaneous center of rotation in the camber plane, wherein such position, during a camber deflection from 0° to 1°, satisfies the following conditions: Y≦0.125*R Z≦−0.0625*R Z≦0.66225*Y+0.02028*R

This application is a continuation of U.S. Ser. No. 11/149,554, now U.S.Pat. No. 7,152,867 issued Dec. 26, 2006, which is a continuation ofInternational PCT/EP03/014066 filed on Dec. 11, 2003, designating theU.S.

BACKGROUND OF THE INVENTION

The present invention concerns the ground contact system of vehicles, inparticular suspension systems and more particularly the guiding of thewheels.

International application WO 01/72572 describes a wheel support devicewhich allows a degree of freedom of the camber of the wheel relative tothe suspension elements. This degree of freedom is controlled eitheractively, for example by a jack as a function of running parameters ofthe vehicle, or passively by the forces exerted on the wheel.

The “wheel plane” means that plane, related to the wheel, which isperpendicular to the wheel axis and passes through the middle of thetyre. The angular position of the wheel plane relative to the body ofthe vehicle is defined by two angles, the camber angle and the steeringangle. The camber angle of a wheel is the angle which, in a transverseplane perpendicular to the ground, separates the wheel plane from themedian plane of the vehicle. This angle is positive when the upper partof the wheel is displaced away from the median plane towards the outsideof the vehicle, and in this case one speaks nowadays of “camber” or“positive camber”. Conversely, when the said angle is negative, onespeaks of “counter-camber” or “negative camber”. In what follows,“camber” or “camber angle” will be used interchangeably.

The steering angle of a wheel is that angle which, in a horizontal planeparallel to the ground, separates the wheel plane from the median planeof the vehicle.

The camber plane is the plane in which the camber takes place. It is thevertical plane, transverse relative to the vehicle and passing throughthe centre of the static contact area. When the steering angle of thewheel is zero, the camber plane contains the axis of the wheel.

In application WO 01/72572 it is proposed for passive systems that theinstantaneous centre of rotation of the camber movement of the wheelrelative to the suspension elements should be located below ground levelso that the transverse forces acting on the contact area generate atorque which tends to tilt the wheel plane in the desired direction(this instantaneous centre of rotation is called the “firstinstantaneous centre of rotation” in the document WO 01/72572). However,although under that condition the transverse forces generate a torque inthe camber axis which tends to tilt the wheel in the desired direction,the efficiency in terms of camber variation is very different dependingon the implemented configurations. In practice, however, the sensitivityof the camber to forces in the contact area is an important criterion.In effect, it is generally sought to design a wheel support andsuspension system such that the passive camber variation is predictable,stable and satisfactory in terms of maximum inclination. This isparticularly important for very high-performance vehicles intendedespecially for racing. For such vehicles the search for absoluteperformance involves optimisation of the longitudinal and transversegrip. This optimisation is only possible if the camber angle of thewheel is at all times close to the ideal for the functioning of thetyre. A camber that is ideal in terms of tyre grip is one that makes itpossible to optimise the homogeneity of the pressure distribution in thecontact area, i.e. which for example allows compensation of the effect,on the pressure distribution in the contact area, of lateraldeformations of the tyre when it is drifting (typically when cornering).

SUMMARY OF THE INVENTION

Thus, one objective of the invention is a wheel support device such asthat described in the document WO 01/72572, whose passive function isimproved.

For this, the invention proposes a support device designed to connect awheel to suspension elements of a vehicle, said wheel of radius ‘R’being designed to rest on the ground, said support device comprisingrods articulated at their lower ends to the suspension elements and attheir upper ends to the wheel carrier, so conferring on said wheel adegree of camber freedom relative to said suspension elements, thecamber movement taking place in the camber plane around an instantaneouscentre of rotation, said device being characterised in that it is alsoconfigured in such manner that, Y and Z being respectively the abscissaand ordinate of the instantaneous position of said instantaneous centreof rotation in the camber plane, said position, during a camberdeflection from 0° to −1°, simultaneously satisfies the followingconditions:

-   Y≦0.125*R-   Z≦−0.0625*R-   Z≦0.66225*Y+0.02028*R

Preferably, the device of the invention is configured such that inaddition, during a camber deflection from 0° to −2°, preferably evenfrom 0° to −3° and preferably even from 0° to −4°, the position of theinstantaneous centre of rotation also satisfies said conditions.

Still more preferably, the support device of the invention is configuredsuch that the position of said instantaneous centre of rotation, in thecase of zero camber, also simultaneously satisfies the followingconditions:

-   −0.125*R≦Y≦0.125*R, and more preferably still −0.0625*R≦Y≦0.0625*R-   Z≦−0.0625*R

Still more preferably, the support device of the invention is configuredsuch that the position of said instantaneous centre of rotation, for acamber of −1°, also satisfies the following condition:

-   Z≦0.66225*Y−0.15*R

Still more preferably, the support device of the invention is configuredsuch that the position of said instantaneous centre of rotation, for acamber of −2°, also satisfies the following condition:

-   Z≦0.66225*Y−0.1625*R

Still more preferably, the support device of the invention is configuredsuch that the position of said instantaneous centre of rotation, for acamber of −3°, also satisfies the following condition:

-   Z≦0.66225*Y−0.1719*R

Still more preferably, the support device of the invention is configuredsuch that the position of said instantaneous centre of rotation, for acamber of −4°, also satisfies the following condition:

-   Z≦0.66225*Y−0.1844*R

Still more preferably, the support device of the invention is configuredsuch that the position of said instantaneous centre of rotation, for acamber of −5°, also satisfies the following condition:

-   Z≦0.66225*Y−0.1969*R

The support device of the invention can be configured such that theposition of the instantaneous centre of rotation, at zero camber, alsosatisfies the condition that Z is greater than or equal to −0.9375*R.

In effect, it emerged surprisingly that the displacement of theinstantaneous centre of rotation during the camber movement must becontained within limits which are the narrower, the larger is the usefulcamber range envisaged.

In a variant of the invention, the support device of the invention isdesigned to be connected to a MacPherson strut.

Preferably, the support device of the invention also comprises controlmeans capable of influencing the camber of the wheel, for example in theform of a damper and/or a spring.

In a preferred embodiment of the invention, the inner rod is connectedon the one hand to the wheel carrier by a pivot joint and on the otherhand to the suspension elements by a swivel joint.

THE DRAWINGS

The invention also concerns a suspension system for a vehicle,comprising the support device described above, and a vehicle with such asuspension system.

FIG. 1 is a longitudinal plan view showing the principle of a suspensionsystem according to the invention.

FIG. 2 is a longitudinal plan view showing the principle of a suspensionsystem according to the invention when the wheel camber is varying.

FIGS. 3, 4, 5 and 6 show examples of kinematic configurations of asupport device according to the invention.

FIGS. 7, 8 and 9 show an embodiment of a suspension system according tothe invention similar to that of FIG. 1.

FIGS. 10, 10 a and 10 b show a suspension system according to theinvention, based on the jointed axle principle.

FIGS. 11, 12 and 13 show an embodiment of a variant of the suspensionsystem of FIG. 10.

FIG. 14 shows an embodiment of the invention based on the rigid axleprinciple.

DESCRIPTION OF A PREFERRED EMBODIMENT

The suspension system 1 of the invention is shown in FIG. 1. Itcomprises various elements designed to maintain the plane PR of a wheel2 relative to the body 5 of a vehicle. The wheel 2, of radius “R”, restson the ground S via its contact area AC. The radius R (also referred toas the “loaded radius”) is the distance between the ground S and thewheel axis when the wheel is vertical and is supporting its rated staticworking load. The wheel carrier 3 is connected to the body 5 by means(4, 6, 7, 8, 9) which allow it two degrees of freedom. The cambermovement of the wheel 2 is allowed by a connection of the wheel carrier3 to the intermediate support 4 via pivoting rods 6 and 7 articulatedwith their lower ends to the suspension elements (4, 8, 9) and withtheir upper ends to the wheel carrier 3. The suspension deflectionmovement is allowed by a connection of the intermediate support 4 to thebody 5 by upper 8 and lower 9 arms (or wishbones). Thus, the suspensionsystem 1 is configured so as to confer on the wheel carrier, relative tothe body 5, on the one hand a degree of freedom of suspension deflectionsince the wheel carrier can undergo essentially vertical movements in amanner known as such, for example in the manner of “multi-arm” or“double wishbone” systems. The suspension spring or other device thatsupports the load has not been shown here.

The support device comprises the wheel carrier 3 and the camber means(the rods 6 and 7). It is this support device which allows the camber ofthe wheel to vary relative to the suspension means.

The camber movement of the wheel carrier 3 relative to the intermediatesupport 4 has an instantaneous centre of rotation (CIR r/s). Theposition of this instantaneous centre of rotation is determined by theintersection of the axes of the rods 6 and 7 connecting the wheelcarrier 3 to the intermediate support 4. FIG. 1 shows the suspensionsystem in a mean position corresponding to the static position of thesuspension system when the vehicle is carrying its rated load on flatground. Here the static camber is represented as essentially zero, i.e.the wheel plane PR corresponds to the vertical plane PV passing throughthe centre of the contact area AC and parallel to the median plane ofthe vehicle. The suspension system 1 includes the support device of theinvention.

FIG. 2 shows the embodiment of FIG. 1 when the wheel 2 adopts a negativecamber angle α (counter-camber). In effect, the wheel plane PR is tiltedtowards the inside of the vehicle at an angle □ relative to the verticalreference plane PV. This inclination can be caused by a transverse forceFy applied within the contact area AC and directed towards the inside ofthe vehicle. This happens to the wheel on the outside of the bend whenthe vehicle is moving along a curved path. In contrast, when the wheelis subjected to a force whose transverse component is directed towardsthe outside of the vehicle (as it is the case for the wheel on theinside of the bend), the component Fy generates a torque which tends topivot the wheel carrier in the direction of increasing camber (i.e. thecamber angle α increases and tends towards positive values).

Camber movements of the wheel carrier can also be “simulated”, i.e.imposed by forces applied to the wheel or directly to the wheel carrierwhile the intermediate support 4 is held fixed relative to the body 5and to the ground S. This allows the kinematic operation of the systemto be checked, measured and analysed.

The instantaneous centre of rotation (CIR r/s) is the point ofintersection of the axes of the rods (6, 7) which define the kinematicsof the movements of the wheel carrier 3 relative to the intermediatesupport 4. The position of that point is variable during cambermovements of the wheel carrier, as can be seen by comparing FIGS. 1 and2. A broken line has been used to show the displacement or evolution ofthe position of the instantaneous centre of rotation (CIR r/s) duringthe camber deflection. According to an essential feature of theinvention, the support device is configured such that the evolution ofthe instantaneous centre of rotation is contained in a well definedportion of the camber plane. This portion A of the camber plane isdelimited by three lines. In fact, the said portion A of the plane is atruncated sector of the camber plane. In the remainder of thisdescription such a portion of the plane will be denoted by the term“sector”. A given sector is thus a part of the camber plane withinwhich, according to the invention, the instantaneous centre of rotationis located during a given camber deflection.

The first sector A represents schematically the zone of the camber planein which, according to the invention, the instantaneous centre ofrotation must be located during a camber deflection from 0° to −1°.

If the device is designed to have a useful camber deflection covering atleast the range from 0° to −2°, the first sector A is also that part ofthe camber plane within which the instantaneous centre of rotationshould preferably be located during a camber deflection from 0° to −2°.

If the device is designed to have a useful camber deflection covering atleast the range from 0° to −3°, the first sector A is also that part ofthe camber plane within which the instantaneous centre of rotationshould preferably be located during a camber deflection from 0° to −3°.

If the device is designed to have a useful camber deflection covering atleast the range from 0° to −4°, the first sector A is also that part ofthe camber plane within which the instantaneous centre of rotationshould preferably be located during a camber deflection from 0° to −4°.

FIG. 2 also shows a zone B. The zone B corresponds to the part of thecamber plane within which the instantaneous centre of rotation shouldpreferably be located when the camber is zero (α=0°). Of course, thezone B is included in the sector A since the position of zero camber isone of the successive positions adopted by the wheel in the camberdeflections envisaged above.

FIG. 2 also shows a second sector C. This sector C corresponds to thatpart of the camber plane within which the instantaneous centre ofrotation should preferably be located for a given counter-camber angle.According to the invention, the larger the useful counter-camberenvisaged, the more restrictive is the criterion concerning thecorresponding position of the instantaneous centre of rotation. Thus,for a counter-camber of −5° the second sector C falls within the secondsector C for a counter-camber of −4, which itself falls within thesecond sector C for a counter-camber of −3°, and so on, until the secondsector C for a counter-camber of −1° which is the widest.

In FIG. 2 the second sector C is for example that corresponding to acounter-camber of −2° (α=−2°) and the displacement of the instantaneouscentre of rotation represented in the figure corresponds to a camberdeflection from 0° to −4° (α=−4°). It can be seen that the entireevolution of the instantaneous centre of rotation is contained withinthe first sector (A), the position corresponding to zero camber (α=0°)is contained within zone B, and the position of the instantaneous centreof rotation when the camber is −2° is contained within the second sector(C) shown.

This graphical representation method allows clear visualisation of thesignificance of the characteristics concerning the evolution of thevarious positions of the instantaneous centre of rotation. Therepresentation is expressed in the form of conditions relating to theCartesian coordinates (horizontal Y and vertical Z) of the instantaneouscentre of rotation in the camber plane.

The various sectors and the zone are open, i.e. they extend to infinity(below ground level). Consequently, the further away the instantaneouscentre of rotation of a configuration is located below ground level, thelarger can be the evolution that is acceptable according to thepreceding criteria. However, secondary criteria such as the track orhalf-track variation, the bulk or the mass of the system will deterthose with knowledge of the field from choosing configurations in whichinstantaneous centre of rotation is too far below ground level.

FIG. 3 represents, in the camber plane, the orthogonal scale (Y-Y, Z-Z)used to characterise the invention. This scale is centred on the onehand upon the vertical plane PV (equivalent to the wheel plane PR whenthe latter is vertical, see FIG. 1) and on the other hand upon thehorizontal plane of the ground S. Thus, the abscissa Y corresponds tothe horizontal position relative to the reference plane PV and theordinate Z corresponds to the vertical position relative to the groundS. The abscissa Y is positive towards the inside of the vehicle andnegative towards the outside. The ordinate Z is positive when the pointconsidered is above the ground S and negative when it is below groundlevel. The axes are graduated in millimetres. In this scale the profilesof the rods 6 and 7 can be marked. The rods are articulated by theirlower ends to the suspension elements (not shown) and by their upperends to the wheel carrier (not shown). As was seen earlier, the movementof the upper part of the rods creates the degree of freedom of thecamber of the wheel carrier relative to the suspension elements. Thecamber movement of the wheel carrier takes place around theinstantaneous centre of rotation (CIR r/s) whose position evolves atevery moment during the camber movement. Thus, the position of theinstantaneous centre of rotation corresponds, throughout the cambermovement, to varying coordinates Y and Z. This variation depends on theposition and orientation of the rods in the camber plane. The graph (inthe same way as FIGS. 1 and 2) can represent a view from behind of theleft part of the suspension of a vehicle. The inside of the vehicle willthen be on the right of the figure and the outside on the left. FIG. 3shows the evolution curve of the instantaneous centre of rotation. Onthis curve are plotted the points corresponding to the position of theinstantaneous centre of rotation for camber angles of 1°, 0°, −1°, −2°,−3° and −4°. The positions of the rods 6 and 7 are represented by fulllines for 0° camber and by broken lines for −4° camber.

In this representation, sector A is the part of the camber planedelimited by the lines DH, DV and DO. The line DH contains all pointswhere Z=Z_(o). The line DV contains all points where Y=Y_(o). Theoblique line DO contains all points where Z=aY+b, “a” being the slope ofDO and “b” being the ordinate at the origin. The sector A can thereforebe defined by the following inequalities:

-   Y≦Y₀-   Z≦Z₀-   Z≦aY+b

According to the invention, the instantaneous centre of rotation islocated along a camber deflection of 0° to −1° and preferably −2°, −3°,−4°. However, if the effective deflection of the device is limited by astop or structural constraint with the same effect, the basicgeometrical configuration of the support device (in particular theposition and orientation of the rods) must, according to the invention,still satisfy the conditions expressed by the sector A, i.e. thedeflection considered can be in part theoretical or virtual.

Preferably, the device of the invention is configured such that when thecamber is zero (α=0°), the instantaneous centre of rotation is locatedin zone B (not shown in this figure for the sake of clarity).

More preferably still, the instantaneous centre of rotation is at adistance smaller than 0.9375*R below ground when the wheel is verticaland carrying its rated static working load. This preferredcharacteristic can also be expressed in the form of an inequalityrelating to the ordinate Z when the camber is zero (α=0°): Z≧−0.9375*R.

FIG. 3 shows the second sector (C) within which the instantaneous centreof rotation should preferably be located when the camber is for example−4°.

As the criterion expressed by the sector C corresponds to an additionalpreferred characteristic in relation to the criterion expressed by thesector A, the second sector C is of course included within the firstsector A.

Zone B and sector C define zones of the camber plane that correspond tocoordinates Y and Z which satisfy conditions different from andadditional to those described earlier for sector A.

The example of FIG. 3 concerns a system whose rods 6 and 7 each have aninteraxial distance (i.e. a distance in the camber plane between thelower and upper articulation axes) of about 200 mm. It can be seen fromthe graph that this configuration satisfies the criteria concerning theevolution from 0° to −4° (sector A) and the criteria concerning theposition of zero camber (sector B). On the other hand, this particularconfiguration does not satisfy the criteria (represented by the secondsector C) concerning the point position corresponding to acounter-camber of −4° but only for −3°. Of course, since the criteriacorresponding to the second sector (C) are the more restrictive, thelarger is the counter-camber concerned (see the description of FIG. 2earlier), the criteria concerning the position of the instantaneouscentre of rotation for a counter-camber of −2° and of −1° are in thiscase also satisfied.

FIG. 4 shows another configuration of the support device of theinvention based on rods 6 and 7 which are shorter (about 100 mm), and aninstantaneous centre of rotation located, for zero camber, a largerdistance below ground level S (about 250 mm). This particularconfiguration gives a greater variation of the position of theinstantaneous centre of rotation. Moreover, the said variation is veryasymmetrical relative to the mean position. In effect, the left-handportion of the evolution curve (i.e. that which corresponds to negativecamber) shows that the instantaneous centre of rotation is moving awayfrom ground level when the wheel tilts in the counter-camber direction(at least for a camber angle between 0° and −3°). In contrast, theright-hand portion of the curve (positive camber) shows that theinstantaneous centre of rotation rapidly approaches ground level whenthe wheel tilts in the camber direction. This configuration, which isvery different from the previous one, nevertheless satisfies thecriterion represented by a sector A identical to the sector A of FIG. 3.

Also schematically shown are the limits C1, C2, C3 and C4 of the sectorsC corresponding to the instantaneous centre of rotation positioncriteria for respective counter-camber angles of −1°, −2°, −3° and −4°.The configuration represented satisfies the criterion corresponding tothe limit C1 since the position of the instantaneous centre of rotationfor a camber of −1° lies within the sector C limited by C1. Similarly,for an angle of −2°, the corresponding position is located in the sectorC limited by C2. On the other hand, in this example the positions forcambers of −3°, −4° and all the more so −5° (not shown) are notcontained within the corresponding sectors C.

FIG. 5 again represents another configuration of the support device ofthe invention based on relatively long rods 6 and 7 (respectively about250 and 300 mm between axes) and an instantaneous centre of rotation,for zero camber, located a still greater distance below ground level S(about 400 mm). This configuration gives a very large and even moreasymmetrical variation of the position of the instantaneous centre ofrotation (compared with the configuration of FIG. 4). Thisconfiguration, which differs from the preceding ones, satisfies thecriteria represented by the sector A and those corresponding to thesector C for each of its limits C1, C2, C3, C4. The criterioncorresponding to zone B (not shown) is of course also satisfied since inthis example, when the camber is zero the instantaneous centre ofrotation is located essentially on the vertical axis Z-Z of the scaleused.

FIG. 6 shows yet another configuration of the support device of theinvention, based on rods 6 and 7 whose interaxial distances arerespectively about 160 and 140 mm and having an instantaneous centre ofrotation at zero camber located about 135 mm below ground level. Thisconfiguration gives a larger camber variation for the wheel on theinside of the bend. In effect, since when cornering the inside wheel issubjected to smaller transverse force than the outside wheel, it may beadvantageous to have a camber sensitivity in relation to transverseforce which is greater for positive than for negative camber angles.This greater sensitivity is obtained by the inclination of the evolutioncurve around the zero camber position. It is clear from the curve thatthe depth of the instantaneous centre of rotation relative to the groundfor a camber of 1° is greater than for a camber angle of −1°. Thispreferred tendency is the converse of those of the configurationsdescribed by FIGS. 4 and 5. The depth difference is even larger ifcamber angles of 2° and −2° are compared, and so on up to 4° and −4°.

A point to be noted is that direct comparison of the graphs shown inFIGS. 3, 4, 5 and 6 can be misleading because the representations usedifferent scales. Moreover, the various sectors are shown schematicallyfor the sole purpose of illustrating the characteristics of theinvention. Their precise definition emerges from the conditions imposedon the coordinates Y and Z of the instantaneous centre of rotation, asdefined in particular in the claims.

FIG. 7 shows an exemplary embodiment of a suspension system according tothe invention designed for a racing vehicle. The suspension comprises anupper wishbone 8 articulated by two swivel joints to the body (notshown) and by one swivel joint to the intermediate support 4, and alower wishbone 9 articulated by two swivel joints to the body and by oneswivel joint to the intermediate support 4. The load is taken up by apush-rod 10 and transmitted, in a manner known as such, to a spring (notshown). A track rod (not shown) controls the steering deflection of theintermediate support 4 relative to the body. The wheel carrier 3 isarticulated relative to the intermediate support 4 via two rods, anouter rod 6 and an inner rod 7. The rods are connected at one end andthe other by swivel joints which define axes or points of articulation.The axes of the rods cross to define the instantaneous centre ofrotation (CIR r/s) close to the wheel plane. Preferably, a control meansin the form of a camber damper 11 controls the camber variations bycontrolling the distance between the upper parts of the wheel carrier 3and the intermediate support 4. A spring can be combined with the damper11 to influence the camber, for example in order to maintain a staticcamber different from that which results solely from the configuration,the load carried by the wheel and the rigidity of the tyre.

FIG. 8 shows the V shape of the inner rod 7 which comprises a lowerswivel joint for its connection to the intermediate support 4 and twoupper swivel joints for its connection to the wheel carrier 3.

FIG. 9 shows the U shape of the outer rod 6 which comprises two lowerswivel joints for its connection to the intermediate support 4 and twoupper swivel joints for its connection to the wheel carrier 3.

This structure corresponds to a preferred embodiment of the inventionwhen applied to the rear, driving axle of a racing vehicle. In thisexample, the spin forces are transmitted from the wheel carrier 3 to theintermediate support 4 via the outer rod 6 alone. Alternatively, theinner rod 7 can also be articulated to the intermediate support 4 by apivot joint (for example by two swivel joints) so that the spin forceswill be taken up conjointly by both rods, which can be advantageous fromthe dimensioning standpoint. On the other hand, since the hyperstaticcharacter of the device increases, its operation will then be moresensitive to the precision of the parallelism between the pivot axes.

FIGS. 10, 10 a and 10 b show schematically a suspension system accordingto the invention which uses the principle (known as such) of a swinginghalf-axle. The degree of suspension deflection freedom is allowed byoscillation of the wishbone 20 relative to the body 5. A push-rod 21 canbe interposed between the triangle 20 and the suspension spring (notshown). The degree of camber freedom of the wheel carrier 3 is allowedby the rods 6 and 7. Thus, the lower wishbone 20 plays the part of theintermediate support 4 (see previous figures) in relation to the wheelcarrier 3. It will be understood that in this case the suspensiondeflection will have an appreciable influence on the configuration ofthe rods because the inclination of the wishbone varies relative to thebody and the ground during the suspension deflection. To the extent thatthe suspension deflection is small (as is often the case in sports orracing vehicles), this influence remains acceptable.

In this example the outer rod 6 is in the shape of U, H or X, i.e. ithas two pivot connections (for example formed by four swivel joints),whereas the inner rod 7 is in the shape of a V, i.e. it has one pivotconnection (to the wheel carrier 3) and one point connection (to thewishbone 20). In this example, the spin forces are transmitted from thewheel carrier 3 to the lower wishbone 20 by the outer rod 6.Alternatively, the inner rod 7 can also be articulated to the lowerwishbone 20 by a pivot connection (for example by two swivel joints) sothat the spin forces are taken up conjointly by both rods, which can beadvantageous from the dimensioning standpoint (see earlier).

FIG. 11 shows an interesting variant of the example embodiment of FIGS.10 to 10 b, designed for the driving rear axle of a racing vehicle. Thedifference is essentially that the spin forces on the wheel carrier 3are transmitted together by the rods 6 and 7 to the lower wishbone 20and also by a slider 19 to a triangle 18. This triangle 18 is connectedto the body in the manner of a suspension wishbone. The articulatedslider 19, orientated transversely to the vehicle, allows for the cambermovement by virtue of its degree of freedom in translation associatedwith a degree of rotational freedom parallel to the camber axis. Thearticulated slider 19 transmits part of the spin forces on the wheelcarrier 3 to the triangle 18 because these forces are directedperpendicularly to the axis of the slider. Thus, the triangle 18 has afunction quite different from the upper wishbone 8 of the device in FIG.7 or of a conventional suspension. Mainly, the triangle 18 allows areduction of the stresses imposed upon the lower wishbone 20 comparedwith the stresses imposed in the embodiment of FIGS. 10 to 10 b. In thiscase a sliding joint 19 with ball bearings has been shown, but manyalternatives could be used.

A camber damper (not shown) can be used for the same purpose as in FIG.7. That damper can be combined with the slider 19.

FIG. 12 shows the V shape of the inner rod 7 comprising a lower swiveljoint for its connection to the lower wishbone 20 and two upper swiveljoints for its connection to the wheel carrier 3. FIG. 13 shows the V orU shape of the outer rod 6 which comprises a lower swivel joint for itsconnection to the lower wishbone 20 and two upper swivel joints for itsconnection to the wheel carrier 3. This combination is made possible bythe fact that part of the spin forces are taken up by the triangle 18.

FIG. 14 represents schematically a vehicle according to the inventionequipped with a suspension system according to the invention. In thisexample the rigid axle suspension principle (known as such) is used. Thedegree of suspension deflection freedom is allowed by the movements ofthe cross-member 22 relative to the body 5. Springs, shown here in theform of spiral springs 23, carry the load. The degree of camber freedomof the wheel carrier 3 is allowed by the rods 6 and 7. An interestingcharacteristic of this combination is that the cross-member 22 remainsessentially parallel to the ground S so that the inclinations of thewheel carrier 3 relative to the cross-member 22 (which plays the part ofthe intermediate support 4 in FIG. 2 or 7) correspond essentially to thecamber variations of the wheel relative to the ground. The suspensiondeflection does not influence the configuration of the rods. A driverigid axle has been shown here (see the transmissions 24). Thesuspension system of the invention can also be applied, of course, inthe case of non-driving rigid axles.

FIGS. 3 to 11 correspond to applications of the invention for a loadedradius R of about 320 mm.

The figures represent particular embodiments of the invention in whichthe instantaneous centre of rotation is contained essentially within thereference plane PV when the camber of the wheel is zero (α=0°), i.e.when the wheel plane PR is vertical. According to the invention, otherconfigurations can be imagined in which the instantaneous centre ofrotation, at zero camber, is away from the plane PV. Preferably, theinstantaneous centre of rotation remains contained within the zone Baimed at. Under rated load the wheel will then tend to adopt a non-zerostatic camber unless corrective measures are taken, for example in theform of one or more springs. Another example of a corrective measure canbe a link (for example mechanical or hydraulic) between the two wheelcarriers of the same axle so as to make the camber movements of the twowheels interdependent. A supplementary effect of such a link is that itcan make the camber movements dependent not only at rest and in astraight line, but also when cornering.

An interesting feature of the invention is that it is applicable to allthe known suspension designs, since supplementary elements can be addedto these existing systems which allow a degree of camber freedom overand above the existing degree of freedom of the suspension. For example,the invention can of course be applied on the basis of MacPhersonsuspension systems or derivatives as described in the application WO01/72572 (corresponding to U.S. Pat. No. 6,688,620) and in particularFIGS. 2 and 3 of that document. In this case the lower portion of thestrut constitutes the intermediate support to which the wheel carrier isarticulated.

The joints of the various elements of the support device or suspensionsystem can be made in various ways. The elastomeric joints currentlyused in the ground contact area can simplify the achievement of systemequilibrium because they introduce given stiffness. On the other handthey are also known to favour the comfort of the vehicle. In the contextof racing vehicles the use of ball joints is preferred for reasons ofguiding precision, weight or bulk. An interesting alternative, known assuch in the context of racing vehicles, consists in the use of flexiblecomposite blades.

To check that a support device or suspension system satisfies a givencriterion concerning the variation of the position of its instantaneouscentre of rotation, the following method can be used:

-   1—The geometry of the system is determined when the suspension is    carrying its rated static load, i.e. the position in the camber    plane of the articulation points of the rods, that of the wheel    plane PR and that of ground level S are determined and the loaded    radius R (for zero camber angle and a tyre at its normal working    pressure) is measured.-   2—The evolution curve of the instantaneous centre of rotation in the    camber plane is constructed (see the examples of FIGS. 3 to 6). This    can be done for example in a theoretical way from the configuration    determined in stage 1. It can also be done experimentally by    artificially imposing the camber variation on the wheel carrier so    as to go through the camber deflection aimed at (for example, from    0° to −3°) and at the same time noting the positions of the rods, so    that the corresponding positions of the instantaneous centre of    rotation can then be deduced from them. To apply the experimental    method, the intermediate support (or the lower triangle, as the case    may be) must be kept immobile relative to the ground S and to the    reference plane PV, for example by fixing it on a measurement bench.    The wheel or tyre is then advantageously taken off. The experimental    method may be limited by the presence of stops or other design    constraints. In that case the theoretical method must be used, at    least for the inaccessible part of the deflection concerned.-   3—The evolution so defined is compared graphically or numerically    with the criteria (sectors A and C and zone B) determined as a    function of the radius R found.

The various geometrical configurations described and illustrated inparticular in FIGS. 3 to 6 are of course applicable in accordance withthe invention to the various possible embodiments, in particular thoseillustrated in FIGS. 7 to 14.

1. Support device connecting a wheel to suspension elements of avehicle, said wheel having a radius ‘R’ and designed to rest on theground, said support device comprising rods articulated at respectivelower ends thereof to the suspension elements and at respective upperends thereof to a wheel carrier to confer on said wheel a degree ofcamber freedom relative to said suspension elements, the camber movementtaking place around an instantaneous centre of rotation, theinstantaneous position of which defined by horizontal and verticalcoordinates Y and Z in a camber plane, said instantaneous position,during a camber deflection from 0° to −1°, simultaneously satisfying thefollowing conditions measured from where the wheel center vertical planecontacts the ground: Y≦0.125*R Z≦−0.0625*R Z≦0.66225*Y+0.02028*R 2.Device according to claim 1, configured such that said conditions arealso satisfied during a camber deflection from 0° to −2°.
 3. Deviceaccording to claim 1, configured such that said conditions are alsosatisfied during a camber deflection from 0° to −3°.
 4. Device accordingto claim 1, configured such that said conditions are also satisfiedduring a camber deflection from 0° to −4°.
 5. Support device accordingto claim 1, configured such that the position of said instantaneouscentre of rotation, at zero camber, also satisfies the followingconditions: −0.125*R≦Y≦0.125*R Z≦−0.0625*R
 6. Support device accordingto claim 5, in which the position of said instantaneous centre ofrotation, at zero camber, also satisfies the following condition:−0.0625*R≦Y≦0.0625*R
 7. Support device according to claim 1, in whichthe position of said instantaneous centre of rotation, at a camber of−1°, also satisfies the following condition: Z≦0.66225*Y−0.15*R 8.Support device according to claim 1, in which the position of saidinstantaneous centre of rotation, at a camber of −2°, also satisfies thefollowing condition: Z≦0.66225*Y−0.1625*R
 9. Support device according toclaim 1, in which the position of said instantaneous centre of rotation,at a camber of −3°, also satisfies the following condition:Z≦0.66225*Y−0.1719*R
 10. Support device according to claim 1, in whichthe position of said instantaneous centre of rotation, at a camber of−4°, also satisfies the following condition: Z≦0.66225*Y−0.1844*R 11.Support device according to claim 1, in which the position of saidinstantaneous centre of rotation, at a camber of −5°, also satisfies thefollowing condition: Z≦0.66225*Y−0.1969*R
 12. Support device accordingto claim 1, configured such that the position of said instantaneouscentre of rotation, at zero camber, also satisfies the followingcondition: Z≧−0.9375*R
 13. Support device according to claim 1,configured such that a vertical distance between ground level and theinstantaneous centre of rotation at a camber of 1° is greater than at acamber of −1°.
 14. Support device according to claim 1, designed to beconnected to a MacPherson strut.
 15. Support device according to claim1, further comprising control means for influencing the camber of thewheel.
 16. Support device according to claim 15, in which the controlmeans comprise a damper.
 17. Support device according to claims 15 or16, in which the control means comprise a spring.
 18. Support deviceaccording to claim 1, in which the an axially innermost one of the rodsis connected on the one hand to the wheel carrier by a pivot joint andon the other hand to the suspension elements by a swivel joint. 19.Suspension system for a vehicle, comprising the support device accordingto claim
 1. 20. Suspension system according to claim 19, also comprisinga rigid axle.
 21. Vehicle comprising a suspension system according toclaim 19.